1. Field of the Invention
The present invention relates to a twin type continuous kneading extruder, and more particularly to a continuous type kneading extruder for continuously performing melting, kneading, degassing and extruding.
2. Description of the Related Art
A conventional twin type continuous kneading extruder for continuously performing melting, kneading, degassing and extruding is shown in Japanese Laid-open Patent Application No. Hei 7-88926. The twin type continuous kneading extruder shown in this publication was invented by the present inventors and the present invention is based on that invention.
The conventional twin type continuous kneading extruder disclosed in that publication includes a twin screw portion in which a first screw shaft and a second screw shaft are arranged rotatably in respective passage portions within a first casing provided with two passage portions continuous with each other and having a cocoon-shaped cross-section. The twin screw portion is provided with two mixing portions.
Each mixing portion is formed by changing a part of each screw shaft from a screw to a mixing rotor. Namely, each mixing portion is constituted by providing the mixing rotor instead of the screw at the same position in the longitudinal direction of each of the two screw shafts.
A single screw portion is provided at a final end portion of the first casing provided with two passage portions to form the twin screw portion. The single screw portion includes a second casing provided with a single passage portion within its interior and connected to the first casing. The passage portion of the second casing is in direct communication with one of the passage portions of the first casing. The single screw is arranged rotatably within the interior thereof and connected directly to the screw shaft disposed in one of the passage portions of the first casing.
The final end portion of the other passage portion of the first casing is in communication with the passage portion of the first casing through a flow rate regulating valve. Accordingly, the molten resin material is introduced into the passage portion of the second casing directly from one of the passage portions of the first casing of the twin screw portion and through the flow rate regulating valve from the other passage of the first casing, respectively.
A vent for degassing under vacuum level in communication with the passage portion of the second casing is provided in the single screw portion, and moisture is degassed from the resin material that is molten and kneaded by the vent. A discharge outlet for discharging the molten resin fed by the screw shafts through the passage portion is provided at the final end portion of the second casing of the single screw portion.
In comparison with the old type well known extruder, the thus constructed conventional twin type continuous kneading extruder is very advantageous in solving the disadvantage that the size of the apparatus is large and the energy consumption is large resulting in poor efficiency, and the defect that it is difficult to clean the complicated screws and cylinders by dismounting or exploding the parts of the screws and cylinders. However, the present inventors have found that, when the twin type continuous kneading extruder is used, the quality of the molten resin fed out from the discharge outlet of the single screw portion has a problem or the capacity of the extruder is disadvantageous. More specifically, although the vacuum degassing is performed in the single screw portion, as a matter of fact, when the molten resin discharged from the discharge outlet is inspected, there is a disadvantage that the vacuum degassing is not sufficiently carried out. Also, the conventional twin type continuous kneading extruder suffers from a problem that the gas generated in the process for melting the resin within the twin screw portion resides in the casing resulting in the poor biting of the material, as a result of which the discharge capacity is degraded.